This invention relates to an electrical regulating circuit. In particular, it provides a regulating circuit for operating a photographic illuminating lamp with regulation of the lamp voltage over a wide range of variations in the amplitude and in the frequency of the input alternating line voltage.
A lamp for photographic illumination often is called upon to produce illumination of specified intensity and specified spectral characteristics in order to produce the desired photographic exposure. An electrical regulator is used to provide the desired stability of lamp voltage, and regulators are known which can accommodate variations in the amplitude or the frequency of the line voltage which powers the lamp. However, photographic illuminators are subject to use throughout the world, and hence are called upon to operate with different and fluctuating values of both voltage and frequency. To meet this requirement in the past has required separate adapters for use with different input powers, or that the operator change switch settings on the regulator.
Further, it is known, for example from the Optoelectronics Manual published by the Semiconductor Products Department of General Electric Corporation, to control the power applied to a lamp to maintain constant brightness over a range of supply voltages. One such circuit controls the charging of a triac-controlling timing capacitor in response to an opto-electric transducer that monitors the output light from the lamp being powered. Other prior publication regarding a. c. voltage regulators for use with lamps, and other devices, include Application Notes AN-509 and AN-527 of Motorolla Semiconductor Products, Inc; Application Notes AN-3886 of the Solid State Division of RCA; and Application Note 200.53 of the Semiconductor Products Department of General Electric. Inc.
U.S. Pat. Nos. 3,952,242 and 3,714,547 also disclose voltage regulators for use with lamps. The former patent regulates the charging of a triac-controlling timing capacitor in response to feedback produced by a lamp connected in parallel with the load and as sensed with an opto-electric transducer. The latter patent employs an operational amplifier to control the triggering of a triac.
However, the prior teachings fail to provide regulators capable of controlling the voltage applied to a lamp under the variations of both amplitude and frequency encountered in line voltages around the world. These line voltages typically range in value between 100 to 240 volts, and range in frequency between 50 and 60 Hertz.
Accordingly, it is an object of the present invention to provide a regulator having this capability. That is, it is an object of the invention to provide a voltage regulator for a photographic lamp suitable for use automatically with a line voltage having a frequency between 50 and 60 Hertz and an amplitude at least between 100 and 240 volts. Such a regulator will be suitable for use with many, if not all, line voltages encountered throughout the world.
It is a further object of the invention to provide a voltage regulator of the above character which is compact, which is relatively light in weight, and which is relatively low in cost. It is also an object that the regulator be safe for the operator to use with minimal risk of electrical shock from the line voltage.
A further object of the invention is that the voltage regulator sustain minimal damage in the event of failure of the lamp being powered, even short circuiting of the lamp.
It is also an object that the voltage regulator operate with high reliability, and correspondingly with relatively high freedom from response to spurious noise signals.
Other objects of the invention will in part be obvious and will in part appear hereinafter.